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Electromagnetic Effects

Shaun Humm

Hi guys, after peoples opinions here, I’ve encountered 6 63A single phase sub main distribution circuits protected by 1361 fuses from a distribution board passing through 3 32mm brass bushes cut virtually on top of each other through the side of two pieces of metallic trunking. The bushes are bridging a change in direction from horizontally to vertically and creating a reduction in trunking size from 9-4 inch. The installation is 3 TP&N and there’s two circuits Allocated per phase. Each two circuits per phase, the line and neutral conductors all pass through one bush together and then like wise for the remaining two phases. There is no slot between the the bushes, and steel locknuts used. 

Although an effort has been made to take all line and neutral conductors for each phase through one hole would this be classed as a non compliance giving its a three phase installation and the amount of current capable of passing through the sub main circuits collectively creating some overheating in the trunking?

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    I read it differently again with two possibilities: (1) L1, L1, 2 x N through bush 1; L2, L2, 2 x N through bush 2; L3, L3, 2 x N through bush 3. Or (2) something like L1, L2, 2 x N through bush 1; L2, L3, 2 x N through bush 2; L3, L1, 2 x N through bush 3. Either way, provided that the neutrals for each circuit go through the same bush as the line conductors for the same circuit, there will be no problem.

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    I read it differently again with two possibilities: (1) L1, L1, 2 x N through bush 1; L2, L2, 2 x N through bush 2; L3, L3, 2 x N through bush 3. Or (2) something like L1, L2, 2 x N through bush 1; L2, L3, 2 x N through bush 2; L3, L1, 2 x N through bush 3. Either way, provided that the neutrals for each circuit go through the same bush as the line conductors for the same circuit, there will be no problem.

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